Centrifugally operated compression release mechanism



April 18, .1967 p FENTON v 3,314,408-

CENTRIFUGALLY OPERATED COMPRESSION RELEASE MECHANISM Filed May 17, 1965 5 Sheets-Sheet l INVENTOR ALVIN P. FENTON ATTORNEY April 18, 1967 A. P. FENTON 3,314,408

CENTRIFUGALLY OPERATED COMPRESSiON RELEASE MECHANISM Filed May 17, 1965 s sheets-sheet 2 Y INVENTOR- ALVIN P- FENTON ATTORNEY April 18, 1967 A P. FENTON 3,314,408

v CENTRIFUGALLY OPERATED COMPRESSION RELEASE MECHANISM Filed m 17, 1965 5 Sheets-Sheet 5 INVENTOR ALVIN P. FENTON ATTORNEV United States Patent 3,314,408 CENTRIFUGALLY OPERATED COMPRESSION RELEASE MECHANISM Alvin P. Fenton, Kohler, Wis., assignor to Kohler Co., Kohler, Wis., a corporation of Wisconsin Filed May 17, 1965, Ser. No. 456,225 13 Claims. (Cl. 123-182) The present invention relates to a compression release mechanism for an internal combustion engine, and more particularly the invention resides in a movable cam surface which is extended into a compression release position when engine speed is below a preset value so as to open an appropriate valve in a compression chamber of the internal combustion engine, such cam surface being retracted when said engine speed exceeds said preset value permitting said valve to close so that the engine will run under full compression.

For many years the art has sought a device for facilitating the starting of internal combustion engines. The primary function of such a device is to reduce the force required to turn over the engine during starting without sacrificing either the conditions necessary lfO'I. reliable and quick starting or power in normal operation. As applied to smaller internal combustion engines, which are intended to be manually started, the chief objective is to minimize the physical exertion required to start the engine and to eliminate the danger of physical injury from kickbacks. As applied to larger engines, the goal is to make possible the use of smaller starting motors requiring less power, and to allow manual starting. Notwithstanding the numerous devices suggested by the art over the years, considerable room for improvement has remained.

Since the chief cause of difliculty in turning over an intern-a1 combustion engine is the engine compression, the prior art shows a multitude of devices for releasing or reducing compression during starting. The most 0bvious, and hence the earliest and most frequently proposed solution to the problem is some form of manually operated or controlled decompression valve, which can be opened during starting and closed after the motor is running under its own power. However, the operation of these valves requires greater skill than the casual operator is likely to have and attention to physical manipulations which an operator might ignore by oversight. The prior art also teaches the use of a tiny, permanently open duct through the compression chamber wall (Patent No. 3,040,725) and a compression release valve which opens during a portion of each compression stroke when the motor is running as well as during starting (Patent No. 2,999,491). Although the prior art teaches that with both of these latter two devices friction and inertia will be sufficient at normal running speeds to prevent excessive power loss, the compression loss during normal operation is nevertheless intolerable for many applications, and in addition it has been found that the small, permanently open ducts readily clog. Finally, the prior art discloses a vast variety of semi-automatic and automatic decompression devices, too numerous to catalogue here, but each of which has failed to provide the desired solution to the problem.

The present invention provides a fully automatic, mechanically operated, compression release mechanism responsive to engine speed to open a decompression valve 3,314,408 Patented Apr. 18, 1967 only during a portion of the compression stroke while starting the engine. This is accomplished by use of a movable cain surface operated in response to centrifugal forces acting upon elements of the structure. By this mechanism, engine compression is automatically reduced until engine speed has reached a predetermined value, as when the engine is either operating under its own power or has enough inertia to carry it through the full compression stroke. When that predetermined engine speed is reached, the present invention automatically terminates this compression release, or decompression so that the engine can run under full compression. The structural simplicity permitted by the present invention in addition to its reliance upon fundamental mechanical forces lend unexpected bonuses of economy, durability, reliability, and broad applicability to this invention.

In a preferred embodiment of the invention the mechanism takes the form of a cam member that is held in a starting, or low speed position, by a centrifugal latch. The cam member and centrifugal latch both rotate in timed relation to engine speed, and the latch is pivoted to swing into and from a latching position holding, or restraining, the cam member in a compression release position. An arm of the centrifugal latch is appropriately weighted so as to cause the latch to pivot from the latching position in response to centrifugal forces developed by the engine, whereby the cam member may move out of its low speed position, to no longer effect a compression release as the engine runs under its own power. The cam member includes a cam surface that may conveniently be located adjacent an exhaust cam for operating an exhaust valve of the engine. When the cam member is in low speed position the cam surface will operate the valve during each compression stroke, and when the cam member moves out of its low speed position the cam surface is then retracted, so as to no longer operate the exhaust valve.

It is an object of the present invention to provide an automatic compression release mechanism to \facilitate and render more safe the starting of internal combustion engines.

It is another object of the present invention to provide an automatic compression release mechanism for an internal combustion engine whereby maximum decompression is achieved during startingof the engine and full high compression is available when the engine is running. It is another object of the present invention to provide an automatic compression release mechanism for an internal combustion engine whereby the need for retarding the spark during starting may be eliminated.

It is another object of the present invention to provide an automatic compression release mechanism for internal combustion engines whereby the cost of the engine may be reduced.

It is another object of the present invention to provide an automatic compression release mechanism for internal combustion engines whereby the size of the magneto in the engine may be reduced.

It is another object of the present invention to provide an automatic compression release mechanism'for an internal combustion engine whereby the size and power requirements of a starter [for the engine may be minimized, and wherein the strain on a starter is reduced.

It is another object of the present invention to provide a completely mechanical automatic compression release mechanism for internal combustion engines that is structurally simple, functionally durable and reliable, compact and inexpensive.

The foregoing and other objects and advantages will appear from the following description of embodiments of the invention shown in the accompanying drawings, which form a part of this disclosure. These embodiments are described in sufficient detail to enable those skilled in the art to practice this invention, but structural changes may be made in the embodiments described, and other embodiments may be used in practicing the invention. Hence, the following detailed description is not to be considered definitive f the scope of the invention, but rather the claims which are found at the conclusion of this specification are to be looked to as particularly pointing out and distinctly claiming the subject matter which is regarded as the invention.

In the drawings:

FIG. 1 is a view in section taken along the line 11 in FIG. 2 of a preferred embodiment of the present invention as mounted in a single cylinder engine,

FIG. 2 is another sectional view of the present invention taken along the line 22 in FIG. 1,

FIG. 3 is a full scale drawing of a timing gear of the internal combustion engine shown in FIGS. 1 and 2 mounting mechanisms of the present invention in starting position,

FIG. 4 shows the mechanism of FIG. 3 in position for normal engine operation,

FIG. 5 is a view of an alternative embodiment showing parts mounted on a timing gear in low speed starting position-s,

FIG. 6 is a view of the embodiment of FIG. 5 showing the parts in running position,

FIG. 7 is a side view of a third embodiment, with the parts in low speed start-ing positions, and

FIG. 8 is an end view of the embodiment of FIG. 7.

Generally speaking, the embodiments illustrated in the drawings show compression release mechanisms operating upon the exhaust valve of a small gasoline engine, so that the exhaust valve will serve a double function as a compression release valve. In these embodiments the compression release valve (exhaust valve) is operated by a nonpositive motion, radial, cam type of mechanism. By disclosing the invention in the environment of the cornparatively simple air cooled \gasoline engine, the entire functioning of the compression release mechanism may be fully and clearly illustrated and the invention thus made manifest may be readily applied to larger or different types of internal combustion engines.

Referring now specifically to the embodiment of FIGS. l-4, there is shown in FIGS. 1 and 2 two cross sectional views of a reciprocating, internal combustion engine 1. An engine block 2 is located above a crankcase 3 and has a head 4 bolted to its top. The engine 1 is a single-cylinder, air-cooled gasoline engine of conventional construction, and it is of the sort that might be used to drive a .small generator, or a sidewalk snow blower, or any of a number of other such familiar machines. Hence, such things as materials used, gaskets, cooling fins and the like require no detailed description here.

A two part cam shaft 5 comprising a quill on a solid rod is journaled in bearings 6 and 7 formed in the walls of the crankcase 3. The cam shaft 5 is of conventional construction and has, as integral parts, an intake cam 8, an exhaust cam 9 and a timing gear 10. Each of the cams 8, 9 is of the radial type, and a cam follower 11 for an intake valve 12 rides on the intake cam 8 and projects through the top of the crankcase 3 into a valve spring housing 13 formed in the block 2. Similarly, :a second cam follower 14 for an exhaust valve 15 rides upon the exhaust earn 9 and projects into the valve spring housing 13.

As can be seen in FIG. 2, the head 4 is shaped to form, together with the space within a cylinder 16 above a recip rocating piston 17, an L-head combustion or compression chamber 18. An intake port 19 and an exhaust port 20 are formed in the block 2 which communicate with the chamber 18. The intake valve 12 is biased downward by a spring 21 to close the intake port 19, and it is periodically raised to open position, for the intake of fuel, by an upward movement of the cam follower 11 in response to the intake cam 8. Similarly, the exhaust valve 15 is biased downward by a spring 22 to close the exhaust port 20, and it is periodically raised to open position by upward movement of the cam follower 14 for exhausting spent gases from the chamber 18. i

As seen in FIG. 2, the piston 17 drives a crank shaft 23, and a gear 24 on the crank shaft 23 engageswith and rotates the timing gear 10, so that the cam shaft 5 together with its parts will be a rotating member driven at a speed proportional to (one-half in this case) crank shaft, or engine speed.

FIGS. 3 and 4 show, on an enlanged scale, a face 25 of the timing gear 10 adjacent the exhaust cam 9. The face 25 rotates with the cam 9 and serves as a convenient mounting surface for mechanism of the invention, but it will be apparent from the following description that this convenience is due in no small part to the proximity in this specific engine 1 of the timing gear 10 to the exhaust cam follower 14, which cooperates with the exhaust earn 9 to open the exhaust valve 15. Mechanism of the invention could alternatively be mounted upon other parts of the rotating cam shaft assembly.

As can be seen in each of FIGS. l-4, a radially movable cam surface 26 projects axially along the cam shaft 5 and away from the face 25 of the timing gear 10, so as to overlap with the surface of the exhaust cam 9. The cam surface 26 faces radially outward and has two primary positions. The first is a radially outward position, as shown in FIGS. l-3, in which it is radially beyond the surface of the exhaust cam 9, so as to "raise the cam follower 14 once during each revolution. This may be termed a low speed or compression release position. The other position is a radially inward position, as shown in FIG. 4, in which it is retracted within a suitable notch in the cam 9. This may be termed a running position.

The movable cam surface 26 is a part of a pivotably mounted auxiliary cam member 30 overlying the face 25 of the timing gear 10, and which swings about a mounting pin 28 projecting from the face 25 of the timing gear 10. The auxiliary cam member 30 is comprised of a cam arm 27, which carries the cam surface 26, and a weight arm 29 that is an integral continuation of the cam arm 27. The weight arm 29 extends from the mounting pin 28 so as to present a mass that is to be acted upon by centrifugal force to actuate the radially movable cam surface 26.

The cam arm 27 and the weight arm 29 extend in divergent directions from the pivot pin 28, so that in the embodiment of FIGS. 1-4 the auxiliary cam member 30 may be described as a centrifugal bell-crank type of class one lever, with centrifugal force upon the weight arm 29 being the working force, the fulcrum being at the mounting pin 28 and the work being done at the radially movable cam surface 26.

The cam arm 27 extends beyond the cam surface 26 to provide a catch finger 31 that engages a starting latch surface 32 of a centrifugal latch 34, next to be described. The entire auxiliary cam member 30 may be formed from fiat stock, and it pivots about an axis parallel to that of the cam shaft 5, so that the motion of any part thereof has a radial component, wherefore there is no need for any linkage joints between its weight arm 29 and the radially movable cam surface 26. Rather, a single, unitary piece is provided.

The centrifugal latch 34 is pivotally mounted on a pin 35 projecting from the face 25 of the timing gear 10 and has sufficient mass to react to centrifugal force developed upon rotation of the cam shaft 5. The free end of the centrifugal latch 34 comprises a holding portion 36 which includes the starting latch surface 32, and a stop pin 33 projects from the face 25 of the timing gear to limit the extent of the radially outward swinging movement of the latch 34 in response to centrifugal force. The centrifugal latch 34, as shown, may be described as a simple class three lever having its fulcrum at the end mounted on pin 35, its work being accomplished at the holding portion 36 and the working force being the centrifugal force acting on the mass between the two ends. In FIG. 3, the latch 34 is shown in a radially inward latching position, and in FIG. 4 it is shown in an outer unlatching position that is assumed in response to centrifugal force. The latch 34, similarly as the auxiliary cam member 30, may conveniently be formed of a single piece of fiat stock, and is pivoted about an axis paralleling that of the cam shaft 5. In this manner the construction of the parts avoids complexity, and lends itself to reliable use in relatively inexpensive engines.

The weight arm 29 and the centrifugal latch 34 are re siliently biased by a wire, torsion type spring 37 wound about the mounting pin 35 and having its ends engaging the outside edges of the arm 29 and latch 34. This resilient bias urges the arm 29 and latch 34 radially inward to the positions of FIG. 3. Hence, when the engine 1 is not running, the torsion spring 37 bears radially inward against the weight arm 29 of the auxiliary cam member 30, pivoting the lever 30 about the pin 28 to force the cam surface 26 radially outward. The spring 37 simultaneously urges the centrifugal latch 34 radially inward, to move the starting latch surface 32 of the holding portion 36 beneath the catch finger 31 extending from the cam arm 27. The low speed position of FIG. 3 is thus assumed when the engine 1 is stopped. The cam surface 26 is extended radially outward, past the surface of the cam 9, and is latched in this position by the starting latch surface 32. When the engine 1 is turned over during starting, the exhaust cam follower 14 will ride up on the radially extended cam surface 26 during a portion of the compression stroke of the piston 17, as shown in FIGS. 1 and 2. This action opens the exhaust valve 15 during that portion of the compression stroke, so as to release the compression developed in the compression chamber 18. Less force is thus required to turn over the engine, than in the case of full compression during starting.

When the engine 1 is accelerated, such as to a speed where the inertia of the engine flywheel will carry it through its entire cycle or where the engine has fired and is turning itself over, the force of the torsion spring 37 on the weight arm 29 and the centrifugal latch 34 is overcome by the centrifugal forces developed. Then, as soon as the centrifugal latch 34 pivots outwardly, under the influence of centrifugal force to the unlatching position of FIG. 4, the surface 32 of the holding portion 36 no longer blocks the catch finger 31. This permits the weight arm 29 to pivot outwardly and swing the centrifugal bell-crank lever 30 in a crisp motion resembling a tripped action. This inward movement is arrested by the back of the movable cam surface 26 engaging the notched cam shaft 5, as shown in FIG. 4. When retracted into its running position, the cam surface 26 is either flush with or beneath the surface of the exhaust cam 9. Thus, it can no longer open the exhaust valve 15 during the compression stroke of the piston 17, and the engine 1 runs under full compression after starting is accomplished.

A primary function of the centrifugal latch 34 is to provide a positive support for the movable cam surface 26. It also provides a sharp cut off of the compression release function at a predetermined engine speed, for without such a latch 34, the termination of the compression release might be gradual, and it might be vacillating in a speed range approaching the predetermined changeover speed. In addition, the latch 34 may be utilized to move the cam surface 26 into and from its compres sion release position, as will be shown in the alternative embodiments of FIGS. 5, 6 and 7, 8.

The force of the torsion spring 37 is balanced against the centrifugal forces developed upon rotation of the centrifugal cam member 30 and centrifugal latch 34, so that operation will occur at a desired speed level. The use of the spring 37 provides a convenient means for varying the preselected change-over speed at which decompression is to cease and full running compression is to be restored. If the spring 37 is made weak, less centrifugal force is required to overcome it and compression release will be terminated at a lower speed. On the other hand, if the spring 37 is strengthened, the opposite result obtains and compression release will occur at higher speeds. Accordingly, the compression release mechanism may be conveniently tailored to any specific need with a minimum of structural change. It is also possible to operate without the spring 37. In such an instance, gravitational force extends the radially movable cam surface 26 into the compression release position of FIGS. 1-3 when the engine 1 is turning over slowly. Then, gravitational force will move the latch 34 inward, to engage the holding portion 36 beneath the catch finger 31. When sufficient engine speed is developed centrifugal forces will operate upon the apparatus to shift to the positions of FIG. 4. However, the spring 37 is expected to add important ingredients to commercial success to the embodiment shown.

Referring now to the embodiment of FIGS. 5 and 6, there is shown a construction in which the auxiliary cam member, here identified by the numeral 38, is not a centrifugally operated member. The cam member 38 is pivoted to a pin 39 on a timing gear 40 of a crankshaft 41, and it includes a radially movable cam surface 42 similar to the cam surface 26 of FIGS. 1-4. A link 43, pivoted at both its ends, joins the catch finger end of the cam member 38 with the holding portion 44 of a centrifugal latch 45 pivoted to a pin 46. A spring 47 biases the latch 45 into the latching position of FIG. 5. The latch 45 in turn, moves the auxiliary cam member 38, through the link 43, into its compression release position.

Upon starting the engine, and gaining suflicient speed, the centrifugal latch 45 will swing outward, and through the link 43 draw the auxiliary cam member 38 into its running position of FIG. 6. The movable cam surface 42 is then retracted from its compression release position.

Another embodiment, shown in FIGS. 7 and 8, moves the auxiliary cam surface in an axial direction to retract it from striking the exhaust cam follower. In this embodiment a pin 48 is extended through a cam shaft 49 to act as a pivot for a centrifugal latch 50. The cen trifugal latch 50 has a weight arm 51 that is normally held in the latching position of FIGS. 7 and 8 by a spring 52. One end of the spring 52 works against a side face' of the exhaust cam 53 and the other end works against the weight arm 51, with the central part of the spring 52 being looped about the pin 48. A movable cam surface 54 is provided on an auxiliary cam member 55 that is integral with the centrifugal latch 50.

For low engine speed the movable cam surface 54 of the auxiliary cam member 55 is in the compression release position of FIGS. 7 and 8, wherein it engages the cam follower 56 during each revolution, at a time when the engine is in its compression stroke. As engine speed increases centrifugal force moves the centrifugal latch 50 in a clockwise direction, as viewed in FIG. 7, to an unlatching position, the center of mass attempting to align in the same axial plane as the pin 48. This movement pivots the auxiliary cam member 55 to retract the movable cam surface 54 axially from under the cam follower 56 into its running position. Thus the third embodiment of FIGS. 7 and 8 uses a centrifugal latch to move an auxiliary cam surface axially from the associated cam follower.

In each of the particular embodiments shown the movable cam surface is in close position to a cam upon which the cam follower for the valve normally rides. The movable cam surface is extended radially beyond this cam during starting, and the only parts required are a centrifugal latch and auxiliary cam member of which the movable cam surface is a part. Hence, the invention provides for a minimal number of parts, and the elimination of complex mechanical connections. As a result, the invention is compact, inexpensive and reliable in operation.

Although the exhaust valve 15 doubles as a compression release valve in the embodiments shown, it may be desirable to have a separate valve functioning solely as a compression release valve, and it is possible also to utilize the intake valve for this purpose. However, use of the intake valve for compression release should, as a general rule, be avoided. Where the intake valve is used as a compression release valve so as to be opened during a portion of the compression cycle a potential fire hazard is created, if the engine should fire before the inertia of the flywheel is sufiicient to carry the engine over top dead center, the engine roll can roll backward and backfire into the carburetor igniting the fuel accumulated there.

Ignition during the compression stroke with the frequently resulting kickback, can be effectively avoided by retarding the spark, but to do this requires substantial added expense, particularly in small engines. The present invention does not seek to prevent early firing, but only to prevent the dangerous kickback from early firing. The open compression release valve reduces pressure so that the engine inertia will carry the engine through the stroke. Also, if there were to be a reversal, or kickback, the pressure would decrease within a few degrees of rotation, due to the venting, so that injurious forces are overcome. By avoiding the need for retarding the spark, the compression release mechanism of the invention effects a substantial cost saving and permits the use of a smaller magneto achieving substantial space saving. Also, by effectively reducing compression during starting, the present invention permits the use of sufliciently small electric starting motors, and opens the possibility of using alternate starter systems. Also, by eliminating kickback fixed timing with its greater precision of control can be employed.

The invention reduces the spark requirement to use lower voltages for firing under the lower compression pressures. Also, the instantaneous speed at the time of ignition due to cranking or starting forces will be greater, so that magneto output is correspondingly increased. In the preferred form of FIGS. 1-4 there is no wear of parts during running, for the latch and cam members rest against stops. Also, it has been found the invention aids in preventing flooding.

By means of the above described embodiments of the invention, the objects and advantages set forth may be accomplished. However, variations in and deviations from the embodiments can be made while still practicing the invention. Various combinations of elements may be utilized to perform in the same manner as the auxiliary cam members and the centrifugal latches described above, and thus the invention may be practiced in other embodiments. Without attempting to exhaust the possible forms in which this invention may be exploited, the foregoing discussion is sufiicientto emphasize that the invention is not limited to the embodiments disclosed here, but rather the subject matter of the invention is set forth in the claims which follow.

I claim:

1. In a compression release mechanism for an internal combustion engine having a compression chamber, a piston that undergoes a compression stroke, a port for the chamber, and a valve with a cam follower for the port, the combination of:

a rotating member that turns in timed relation to engine speed;

a cam face on said rotating member upon which said cam follower rides;

an auxiliary cam member rotatable with said rotating member that is shiftable, with respect to the rotating member, between a low speed position and a running position;

a centrifugal latch carried by said rotating member to turn therewith, which latch is pivotally mounted on the rotating member and has a weight arm portion to move radially in response to centrifugal force from a latching position to an unlatching position, said centrifugal latch holding said auxiliary cam member in said low speed position when in its latching position; and

a movable cam surface on said auxiliary cam member which is projected into a compression release position that engages said cam follower during a compression stroke when said auxiliary cam member is in its low speed position, and which retracts from its compression release position when said auxiliary cam member is in its running position.

2. In a compression release mechanism for an internal combustion engine having a compression chamber, a piston that undergoes a compression stroke, a port for the chamber, and a valve with a cam follower for the port, the combination of:

a rotating member that turns in timed relation to engine speed;

a cam face on said rotating member upon which said cam follower rides;

a centrifugal latch having a holding portion that is pivoted upon said rotating member to turn therewith and which pivots, with respect to the rotating member, about an axis substantially parallel to the axis of rotation of said rotating member to thereby move in response to centrifugal force from a low speed latching position to an unlatching position to correspondingly shift said holding portion in its position;

an auxiliary cam member rotatable with said rotating member that is shiftable, with respect to the rotating member, between a low speed position and a running position, said auxiliary cam member being blocked from movement into its running position by the holding portion of said centrifugal latch when said latch is in its low speed latching position; and

a movable cam surface on said auxiliary cam member which has a compression release position, assumed when said auxiliary cam member is in low speed position, which is radially outward from said cam face to engage said cam follower during a compression stroke, and which retreats from such compression release position when said auxiliary cam member is in its running position.

3. In a compression release mechanism for an internal combustion engine the combination comprising:

a rotatable mounting member to be driven by the engine;

a centrifugal latch pivoted upon said mounting mem her that is radially displaceable in response to centrifugal force developed by rotation of said mounting member;

a holding portion on said centrifugal latch that is moved from a blocking position upon displacement of the latch in response to centrifugal force;

a centrifugal cam member supported upon said mounting member that is displaceable, in response to centrifugal foroe developed by rotation of said mounting member, and which has a movable cam surface that shifts radially with respect to the axis of rotation of said mounting member upon displacement of said centrifugal cam member; and

said centrifugal cam member having a catch portion engageable with said holding portion of said centrifugal latch to be arrested thereby until there is a displacement of said centrifugal latch in response to centrifugal force.

4. A compression release mechanism as in claim 3 having resilient bias means acting upon said centrifugal latch and said centrifugal cam member in directions opposite the action of centrifugal force.

5. In a compression release mechanism for an internal combustion engine the combination comprising:

a rotatable mounting member;

a centrifugal cam lever pivoted upon said mounting member at a point intermediate its ends with a weight arm responsive to centrifugal force to one side of the pivot and a radially movable cam surface to the other side of the pivot, which cam surface is radially retracted upon swinging motion of said weight arm in response to centrifugal force;

a centrifugal latch pivoted upon said mounting member in the form of a lever with sufficient mass to swing the latch outward in response to centrifugal force and having a holding portion that blocks pivot of said centrifugal cam lever when said latch is in inward position; and

valve means responsive .to said cam surface when in a radially outward position.

6. A compression release mechanism as in claim 5 having resilient bias means urging said centrifugal cam lever to pivot in a direction placing said cam surface in a radial outward position, and urging said centrifugal latch to its inward position.

7. In a compression release mechanism for an internal combustion engine, the combination comprising:

a rotatable cam shaft to be driven at a speed proportional to engine speed;

a cam surface mounted to rotate with said cam shaft and radially movable with respect to said shaft;

a compression release valve responsive to the radial position of said cam surface;

a movable latch mounted to rotate with said cam shaft and pivoted for movement in a plane radial of said cam shaft, said latch having mass adapted to be moved radially outward by centrifugal force when engine speed attains a preset minimum value;

a holding portion on said movavble latch that is swung from a latching position to an unlatching position upon said latch moving in response to centrifugal force; and

said cam surface being held radially outward by said holding portion in a compression release position, and being retractable upon said holding portion being swung to its unlatching position.

8. :In a compression release mechanism for an internal combustion engine, the combination comprising:

a rotatable cam shaft to be driven at a speed proportional to engine speed;

a centrifugal cam member mounted to rotate with said cam shaft about a cam shaft axis and pivoted for pivot in a plane substantially perpendicular to the cam shaft axis, said cam member having a radially movable cam surface and a radially movable weight so that when engine speed is below a preset minimum said cam surface is extended radially outward and when engine speed exceeds said preset minimum said weight is moved by centrifugal force radially outward to cause said cam surface to be retracted radially inward; and

a compression release valve adapted to be opened during at least a portion of each compression stroke of said engine by said movable cam surface when said cam surface is extended radially outward.

9. A compression release mechanism for an internal combustion engine having a compression chamber and a compression release valve in a port communicating with said compression chamber for releasing compressed fluids in said chamber, the combination comprising:

a radially movable cam arm and a radially movable weight arm joined together and mounted on a pivot that rotates about an axis in said engine at a speed proportional to the speed of said engine, said pivot providing for limited radial movement of both said cam arm and said weight arm with respect to said axis such that when said Weight arm moves radially inward said cam arm is extended radially outward and when said weight arm moves outward said cam arm is retracted radially inward;

said compression release valve being mechanically engageable with said movable cam arm to open said port during a compression stroke of said engine when said cam arm is extended radially; and

a centrifugally movable latching member mounted on a second pivot that also rotates about said axis to positively support said cam arm in its radially outward extended position and to be moved by centrifugal force about the second pivot to release said cam arm when the engine exceeds a preset speed.

10. In a compression release mechanism to operate in conjunction with a cam shaft of an internal combustion engine to actuate a compression release valve during part of a compression stroke of said engine during starting, the combination comprising:

a cam shaft of an internal combustion engine;

a cam member carried by said cam shaft having a movable cam surface at one end projecting radially from said cam shaft, and being movably mounted on said cam shaft to retract said cam surface with respect to said cam shaft;

a latch having a holding portion and being pivotally mounted bysaid cam shaft so that said holding port-ion can engage said cam member to positively support said cam surface in a radially extended position during starting and can pivot to disengage s-aid cam member when said engine exceeds a preset speed; and

a spring urging said latch into position for said holding portion to engage said cam member.

'11. In a compression release for an internal combustion engine having a port communicating between the compression chamber and an external atmosphere, a valve mounted to close and open said'port, a rotatable cam for operating the valve, and a timing gear that rotates the cam and is positioned alongside thereof, the combination therewith of:

an auxiliary cam member mounted for rotation with said cam and having a radially movable cam surface projecting into the plane of rotation of said cam;

a centrifugal latch pivotally mounted at one end thereof to said face of said timing gear and having a holding portion to support said auxiliary cam member with said 0am surface in a radially outward position at slow speeds of rotation; and

spring means engaging said centrifugal latch urging said latch radially inward, and being of such spring force as to be overcome by centrifugal force operating on said latch at a predetermined engine speed, so as to move said holding portion of said latch from said auxiliary cam member to permit said cam surface to be moved radially inward.

1 2. An apparatus as in claim ill, wherein the holding portion of said centrifugal latch and said auxiliary cam member are connected by a linkage.

|13. In a compression release mechanism for an internal combustion engine having a compression chamber, a piston that undergoes a compression stroke, a port for the chamber, and a valve with a cam follower for the port, the combination of:

a rotating member that turns in timed relation to engine speed;

a cam face on said rotating member upon which said cam follower rides;

a centrifugal latch carried by said rotating member to turn therewith, which latch is movably mounted about an axis transverse to the axis of said rotating compression release position when said auxiliary cam member to move in response to centrifugal force member is in its running position; and 7 from a latching position to an unlatching position; spring means biasing said centrifugal latch to its an auxiliary cam member connected to an end of said latching position.

centrifugal latch that is shiftable along the axis of 5 said rotating member between a low speed position References Cited by the Examiner and arunning position, said centrifugal latch hold- UNITED STATES PATENTS mg said auxiliary cam in said low speed posltion when in its latching position; 868,765 10/1907 "Dock 23 182 a movable earn surface on said auxiliary cam member 10 1,729,636 9/ 1918 Bender X which projects into a compression release position for engaging said cam follower during a compres- MARK NEWMAN, Przmary Examiner.

sion stroke when said auxiliary cam member is in its low speed position, and which retreats from its RADPH BLAKESLEE Examiner 

8. IN A COMPRESSION RELEASE MECHANISM FOR AN INTERNAL COMBUSTION ENGINE, THE COMBINATION COMPRISING: A ROTATABLE CAM SHAFT TO BE DRIVEN AT A SPEED PROPORTIONAL TO ENGINE SPEED; A CENTRIFUGAL CAM MEMBER MOUNTED TO ROTATE WITH SAID CAM SHAFT ABOUT A CAM SHAFT AXIS AND PIVOTED FOR PIVOT IN A PLANE SUBSTANTIALLY PERPENDICULAR TO THE CAM SHAFT AXIS, SAID CAM MEMBER HAVING A RADIALLY MOVABLE CAM SURFACE AND A RADIALLY MOVABLE WEIGHT SO THAT WHEN ENGINE SPEED IS BELOW A PRESET MINIMUM SAID CAM SURFACE IS EXTENDED RADIALLY OUTWARD AND 